The invention relates to a threaded bolt provided with measurement planes for use in ultrasonic length measurement. More specifically, after the threaded bolt has been used to form a connection, a measurement is taken to determine the length change of the threaded bolt, and therefore determine the tension within the threaded bolt.
It is known to provide a threaded bolt with measurement planes. Typically, the measurement planes are formed either at a recess or an elevation with respect to the actual end planes of both the head end and the insertion end. The measurement planes are often formed by means of cold deformation and finishing. One such threaded bolt is described in European patent application 0,459,365 which issued May 28, 1991, the contents of which are incorporated herein by reference.
Another threaded bolt is known from U.S. Pat. No. 4,846,001 which issued Jul. 11, 1989, in which the threaded bolt is shown as having a head which has been provided with a recess including a measurement plane. The measurement plane has been made sufficiently smooth/level by finishing, in order to be used in ultrasonic measuring. The recess is used for accommodating a piezoelectric sensor. In another embodiment the recess is absent and the sensor is placed on top of the end plane at the head.
Frequently, existing threaded bolts exhibit several radial planes at one or both ends, situated at various axial distances measured along the centerline of the threaded bolt, which can adversely affect the ability to achieve accurate measurement results.
It is an object of the invention to reduce the number of radial planes exhibited by the threaded bolt, thereby improving the accuracy with which ultrasonic length measurements on the bolt can be performed.
One embodiment of the invention provides a threaded bolt having a proximal head end and a distal insertion end, wherein the proximal head end and the distal insertion end have been provided with a single, exposed radial measurement plane for use in ultrasonic length measurement in order to determine the tension in the threaded bolt after it has been used in a connection. The measurement plane at the distal insertion end is formed by the flat bottom of a recess at the distal insertion end, wherein the recess is bounded by a circumferential wall. The circumferential wall transitions into the flank of the distal insertion end via a buckle or curve. Therefore, multiple radial planes at the insertion end other than the measurement plane are prevented. Therefore, the ultrasonic length measurement is related only to the measurement plane at that location and double signals are prevented. The measurement plane is protected from pollution and damage by the recess.
Another embodiment of the invention provides a threaded bolt having a proximal head end and a distal insertion end, wherein the proximal head end and the distal insertion end have been provided with a single, exposed radial measurement plane for use in ultrasonic length measurement in order to determine the tension in the threaded bolt after it has been used in a connection. The measurement plane at the distal insertion end is formed by the flat bottom of a recess at the distal insertion end, wherein the recess is bounded by a circumferential wall and the outermost distal end of the threaded bolt is formed by a circular line.
In preferred embodiments, the transition from the circumferential wall of the recess into the flank of the distal insertion end may run according to a convex course, but preferably has a sharp buckle shape, thereby ruling out the occurrence of murmur while taking measurements as much as possible.
Preferably the circumferential wall of the recess forms a conical surface which is oblique with respect to the bolt center line, the angle of which is maximally 75xc2x0 with respect to the bolt center line, preferably also more than 45xc2x0.
Preferably the flank in the distal end portion, which is contiguous to the circumferential wall of the recess, forms a flank conical surface oblique with respect to the bolt center line, the angle of which is maximally 45xc2x0 with respect to the bolt center line. Preferably the flank conical surface at the proximal side changes into the cylindrical plane via a flank conical surface which is less oblique with respect to the bolt center line, for instance at 25-35xc2x0, which cylindrical plane may or may not be contiguously provided with the thread. Alternatively, the distal end of the bolt provided with the aforementioned recess is truncated at the flank.
Preferably the recess has been formed by means of an upsetting treatment of the insertion end. As a result of the upsetting treatment, the distal end of the bolt can be provided with its final form in one step. Alternatively, apart from the upsetting treatment for forming the recess, the oblique flank can be obtained by means of a machining treatment.
It is a further object of the invention to provide a threaded bolt which can easily be manufactured and is able to provide reliable measurement results.
To that end, a preferred embodiment of the invention provides a threaded bolt having a proximal head end and a distal insertion end, the proximal head end and the distal insertion end being provided with measurement planes for use in ultrasonic length measurement in order to determine the tension in the threaded bolt after it has been used in a connection. The measurement plane at the insertion end forms the complete end plane and has been arranged on the insertion end without a final processing operation.
In preferred embodiments, the measurement plane has been arranged at the distal insertion end by means of an upsetting treatment. The upsetting treatment can advantageously be performed during a heading treatment performed in a bolt machine, also known as xe2x80x9cbolt makerxe2x80x9d. In such a bolt machine, the upsetting of the head takes place in one operation. During the upsetting treatment, the measurement planes can be realised at both ends. Therefore, the exact axial distance between both measurement planes can be determined.
Alternatively, the upsetting operation for making the measurement planes may take place during the subsequent shank reduction.
By way of a further alternative, instead of by means of the upsetting treatment, the measurement plane at the insertion end can be made in the same bolt machine, but in a following station, where the point is made. This then takes place by means of a machining treatment.
The invention furthermore provides a method for manufacturing a threaded bolt according to the invention.